A photolithography tool is a device for exposing a mask pattern onto a wafer, primarily used in the fabrication of integrated circuits (ICs) and other micro-devices. During the exposure of the mask pattern, the mask and wafer are moved simultaneously relative to a projection system and a projection light beam.
Increasing integration of large-scale IC devices leads to demand for photolithography tools with higher resolutions and smaller critical dimensions. At present, photolithography tools have evolved into combinations of internal and external worlds. In such a photolithography tool, a wafer stage, a mask stage and an illumination system for them are damped as three independent worlds. For a fine-motion module, effective damping of a wafer chuck or a mask chuck is necessary for immunizing it from influences from other system during exposure. Gravity compensators are new apparatuses developed in such a context, which accomplish leveling and focusing of the wafer or mask chuck by use of active or passive damping techniques, thus allowing the fine-motion module to operate as an independent internal world.
An existing magnetic gravity compensator is shown in FIG. 1, which employs a mechanical gravity compensation structure having a vertical static gravity compensation module constructed of a leaf spring 1′, a movable bottom plate 2′ and a tension spring (not shown). The structure additionally has a connection block 3′ capable of adjustments in the RX/RY degree of freedom, which damps the fine-motion stage 4′ by being connected to it. However, as this solution requires three such magnetic gravity compensators to support the fine-motion stage 4′, it is difficult to equally divide the gravitational load among them. The solution also suffers from high structural complexity, high stiffness requirements, low controllability and low accuracy.
In order to address these problems, there has been proposed later a voice coil motor, as shown in FIG. 2, which is capable of magnetic gravity compensation. With the motor, a static force is generated between a stator magnet group 5′ and a rotor magnet group 6′ for balancing the gravity of a motion component. In addition, the powerful voice coil motor is capable of adjustments in the gravity compensation so as to achieve an adjustment of the thrust force. However, this solution is associated with a number of problems such as heavy heat generation and a limited range of adjustment in the compensation provided by the voice coil motor.